This invention concerns new nitrogen-containing additives useful as agents for lowering the cloud point of hydrocarbons middle distillates (fuel-oils, gas oils) as well as the middle distillates compositions containing said additives.
The oil distillates of the invention are middle distillates (fuel oil, gas oil) distilling in the range (ASTM standard D 86-67) from 150.degree. to 450.degree. C. The gas oils more particularly concerned are those distilling in the range from an initial temperature comprised between 160.degree. C. and 190.degree. C. to a final temperature comprised between 350.degree. C. and 390.degree. C.
A large number of products available on the market are recommended for improving the limit filterability temperature and the pour point of oil cuts of high paraffin content, such as:
polymers basically formed of long chain olefins PA1 co-polymers basically formed of alpha-olefins PA1 ethylene-vinyl acetate copolymers PA1 N-acylaminoethylesters of acid-containing polymers, or PA1 halocarbon compounds
These products act on the crystallization kinetic phenomena and modify the crystal size, thereby making possible the use of the suspension at a lower temperature without clogging of the pipes and the filters. The above-mentioned products do not change the temperature at which the first paraffin crystals become apparent. As a matter of fact it has been considered, up to now, that this temperature was dependent on the molecular weight and the formula of the paraffins and on the nature of the solvent.
The lowering of the cloud point of the middle distillates (particularly the gas oils) by means of an additive, would be of particular interest in the refinery industry since it would make it possible, without changing the distillation flowsheet, to meet the specifications, which are now evolving towards a greater severity.
It has now been discovered that certain chemical compounds which are defined hereinafter have the property, when added to middle distillates, to limit the appearance of the first paraffin crystals to a temperature lower than that at which they would appear in the absence of such additives. This property is the more unexpected as it is maintained after several heating and cooling cycles and its mechanism has not yet been explained.
This category of chemical products also has an effect on other properties of the middle distillates (particularly gas oils) by modifying the behavior of the medium containing the precipitated paraffins.
Thus the compounds recommended according to the invention have a substantial action on the filterability limit temperature and the pour point.
When the paraffin crystals, whose formation results from the cooling, have appeared, they naturally tend to gather by gravity in the bottom portion. This phenomenon, generally called sedimentation, results in the clogging of the pipes and filters and is detrimental to the convenient use of the middle distillates particularly of the gas oils. The chemical compounds recommended according to the invention are able to substantially decrease the sedimentation rate of the paraffins formed by cooling gas oils or other middle distillates.
Finally, the products recommended for their above-mentioned properties further confer to the gas oils and middle distillates to which they are added, anti-corrosion properties on metal surfaces.